linux-kernel - Re: [PATCH RFC] KVM: TDX: Defer guest memory removal to decrease shutdown time

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Message-ID: <2a25d2c8-6b2e-443b-98aa-723dea2c9e78@intel.com>
Date: Thu, 13 Mar 2025 21:07:15 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: <seanjc@...gle.com>, <kvm@...r.kernel.org>, <rick.p.edgecombe@...el.com>,
	<kirill.shutemov@...ux.intel.com>, <kai.huang@...el.com>,
	<reinette.chatre@...el.com>, <xiaoyao.li@...el.com>,
	<tony.lindgren@...ux.intel.com>, <binbin.wu@...ux.intel.com>,
	<isaku.yamahata@...el.com>, <linux-kernel@...r.kernel.org>,
	<yan.y.zhao@...el.com>, <chao.gao@...el.com>
Subject: Re: [PATCH RFC] KVM: TDX: Defer guest memory removal to decrease
 shutdown time

On 13/03/25 20:39, Paolo Bonzini wrote:
> On Thu, Mar 13, 2025 at 7:16 PM Adrian Hunter <adrian.hunter@...el.com> wrote:
>> Improve TDX shutdown performance by adding a more efficient shutdown
>> operation at the cost of adding separate branches for the TDX MMU
>> operations for normal runtime and shutdown.  This more efficient method was
>> previously used in earlier versions of the TDX patches, but was removed to
>> simplify the initial upstreaming.  This is an RFC, and still needs a proper
>> upstream commit log. It is intended to be an eventual follow up to base
>> support.
> 
> In the latest code the HKID is released in kvm_arch_pre_destroy_vm().

I am looking at kvm-coco-queue

> That is before kvm_free_memslot() calls kvm_gmem_unbind(), which
> results in fput() and hence kvm_gmem_release().
> 
> So, as long as userspace doesn't remove the memslots and close the
> guestmemfds, shouldn't the TD_TEARDOWN method be usable?

kvm_arch_pre_destroy_vm() is called from kvm_destroy_vm()
which won't happen before kvm_gmem_release() calls
kvm_put_kvm().